A technique has hitherto been known which minimizes the entrance of foreign substances from outside into a sealing structure that has a torsional vibration damper and an oil seal, by providing a labyrinth structure in the sealing structure. One example of such a structure will be described with reference to FIG. 3. FIG. 3 is a schematic cross-sectional view of a sealing structure according to a prior art example.
As shown, the torsional vibration damper 600 includes a tubular part 610 that is attached to a crankshaft 300. The oil seal 500 includes a reinforcing ring 510 and a sealing body 520 made of an elastic material and formed integrally with the reinforcing ring 510. The reinforcing ring 510 includes a cylindrical part 511, and an inward flange part 512 provided at an end on the opposite side from the sealed-fluid side of this cylindrical part 511. The sealing body 520 includes an oil lip 521 provided such as to be slidable on an outer circumferential surface of the tubular part 610, and a dust lip 522 provided further on the opposite side from the sealed-fluid side than the oil lip 521 and slidable on the outer circumferential surface of the tubular part 610.
In addition, a side lip 523 is provided to the sealing body 520 in this prior art example. This side lip 523 is configured to increase in diameter toward the opposite side from the sealed-fluid side so that foreign substances do not easily enter the sliding part between the dust lip 522 and the outer circumferential surface of the tubular part 610 from the air side. An annular groove 621 is formed in a body part 620 of the torsional vibration damper 600. The side lip 523 is disposed such as to extend into this annular groove 621. This way, a confined and complex path is formed from the air side to the sliding part between the dust lip 522 and the outer circumferential surface of the tubular part 610. A labyrinth structure is thus provided.
In some cases where there is only a small space available for mounting the oil seal 500, the inward flange part 512 of the reinforcing ring 510 has to be made shorter. In such cases, it may not be possible to adopt the side lip 523 configured as described above. The reason therefor is explained below.
The oil seal 500 is fabricated by insert-molding the sealing body 520, with the reinforcing ring 510 serving as the insert component. In this process, the sealing body 520 is formed, with the reinforcing ring 510 being set in position in the metal mold. The resultant sealing body 520 has an opening 524, which leads to an end face of the inward flange part 512 of the reinforcing ring 510 on the opposite side from the sealed-fluid side. That is, the opening 524 is formed in a portion corresponding to a support part (not shown) provided in the metal mold for the positioning purpose. Therefore, the portion on the end face of the inward flange part 512 of the reinforcing ring 510 on the opposite side from the sealed-fluid side is exposed. This exposed portion is utilized when mounting the oil seal 500. Namely, when mounting the oil seal 500, it is pressed with a jig or the like. If the sealing body 520 that is made of an elastic material is pressed, it may be damaged or broken, so that the reinforcing ring 510 is pressed instead, through the opening 524.
If the inward flange part 512 of the reinforcing ring 510 is short and the side lip 523 is configured to increase in diameter toward the opposite side from the sealed-fluid side, the opening 524 may be blocked by the side lip 523. If this is the case, the reinforcing ring 510 cannot be pressed with a jig or the like through the opening 524.
During transportation, a plurality of oil seals 500 are stacked on one another along the center axis direction. In the case with the oil seal 500 shown in FIG. 3, when a plurality of the oil seals 500 are stacked on one another, the side lips 523 fit in the annular gaps between the oil lips 521 and the cylindrical parts 511 of the reinforcing rings 510 of adjacent oil seals 500. Thus the plurality of oil seals 500 can be snugly stacked on one another. However, if the inward flange part 512 of the reinforcing ring 510 is short and the side lip 523 is configured to increase in diameter toward the opposite side from the sealed-fluid side, the side lip 523 may, depending on size, abut a portion of the reinforcing ring 510 of the adjacent oil seal 500, near the distal end of the cylindrical part 511 of the reinforcing ring 510. In this case, the plurality of oil seals 500 cannot be stacked on one another.
Further, the body part 620 of the torsional vibration damper 600 needs to be sufficiently thick so as to form the annular groove 621 for providing the labyrinth structure. This increases the weight of the body part 620 of the torsional vibration damper 600. Also, since the body part 620 is typically a cast product so that the annular groove 621 has to be formed by a cutting process, which is another impediment to cost reduction.